Hood-shaped support frame for a low cost virtual reality system

ABSTRACT

Apparatus is disclosed for viewing computer generated images and for tracking the positions of the user&#39;s head and hand. One alternative of the apparatus includes a frame element, versatilely mountable, with sensors for the head tracking of a user whose bodily movement is constrained to a small area. Short range and inexpensive sensors are deployed for tracking the position of the user&#39;s head; these sensors are deployed partly on a on the user&#39;s head and partly on the tracking frame. All the electronics for tracking and user input are enclosed in a mobile pack. In another alternative of the tracking invention natural forces such as gravity, the Earth&#39;s magnetic field, and inertia are used, so additional references. The display allows for interchangeable optical elements so that it may be tailored to suit the needs of a particular user or application. One optical element disclosed is a bicolor polarizer, which allows an lcd to inexpensively provide a bicolor display without loss of resolution.

This application is a continuation of U.S. application Ser. No.08/319,026 entitled `Low Cost Virtual Reality System,` filed Oct. 6,1994, by Ann Lasko-Harvill, Michael A. Teitel and Jaron Z. Lanier U.S.Pat. No. 5,850,201, which is a continuation of abandoned U.S.application Ser. No. 08/165,045 entitled `Low Cost Virtual RealitySystem,` filed Oct. 6, 1993, by Ann Lasko-Harvill, Michael A. Teitel andJaron Z. Lanier, which is a continuation of abandoned U.S. applicationSer. No. 07/888,472 entitled `Low Cost Virtual Reality System,` filedMay 21, 1992, by Ann Lasko-Harvill, Michael A. Teitel and Jaron Z.Lanier, which is a continuation of abandoned U.S. application Ser. No.07/621,117 entitled `Low Cost Virtual Reality System,` filed November30, 1990, by Ann Lasko-Harvill, Michael A. Teitel and Jaron Z. Lanier.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of devices for dataentry, viewing, and manipulation in computers. More particularly, thisinvention relates to a low cost human interface system for interactivecomputer simulations, most particularly a low cost human interface for avirtual reality system.

Three of the key aspects of a virtual reality interface are tracking theuser's head and other body parts, sensing user input actions and displayof sensory information to the user in such a way that the sensoryinformation displayed replaces the corresponding senses arising from thephysical world. Such systems are typically quite expensive.

Position and orientation of the user's head and other body parts arecontinually tracked in order to keep the simulation updated tocorrespond correctly to the user's changing point of view. Trackingtechnologies have been relatively high cost components of a virtualreality system, and typically involve electromagnetictransmitter/receiver systems such as manufactured by Polhemus Inc., ofColchester, Vt.

The display of sensory information from the virtual reality simulationmust be proximal to the user's head at all times, so that the relativeposition of the display to the user's eyes and ears remains constant asthe user moves. Such a system is generally termed a Head Mounted Display(HMD), though it is not limited to devices mounted directly on the head.It contains visual and auditory displays for each sense organ and hastypically also been an expensive component.

Of particular interest here is the visual display portion of the HMD.Weight concerns generally dictate a liquid crystal display (lcd). Thegeneral structure of a lcd display includes a source of unpolarizedlight, a first polarizer, a polarization rotating array (which createsthe individual pixels), and a second polarizer which serves as ananalyzer. Light travels in the above named sequence. The first polarizergives the light a uniform polarization, either in the angle transmittedby the analyzer or perpendicular to it. The polarization rotating arrayoperates on the polarized light in a pixel-wise manner, either passingit unchanged or rotating the polarization by 90°. This light thencontinues on to the analyzer, which in one polarization angle transmitsall wavelengths, and perpendicular to that blocks all wavelengths, toleave light: and dark pixels for display. Since in an HMD the pixels areso close to the viewer's eye, many people focus on the pixels at anindividual level and don't perceive the overall shapes within the imageas well. For this reason a diffusion screen may be superimposed over thelcd, which slightly blurs the image and fine detail, but facilitates theperception of patterns and shapes. Understandably, not all viewers likethis trade off.

Color lcds can be made by including a mask within the display, dyed withred, blue and green pixel sized dots. This-mask is lined up with thepixels of the polarization rotating array, and each grouping of threemonochromatic pixels masked to form a red, blue and green pixel thenforms a color pixel. This conversion to a color lcd obviously results ina 3:1 reduction in resolution.

Color versus resolution is just one of the many trade-offs that must beresolved in choosing a display. Another important consideration iswhether and how much the fields of view of the right and left eyesoverlap. The most natural classification is into two groups--separateimages for each eye and totally shared images. Using separate images foreach eye instead of a totally shared image has the advantage of allowingstereoscopic vision and improved depth perception. Unfortunately, havingtwo separate images requires more computing power, and for an lcd ofgiven pixel size and distance from the eye only half as many pixels areavailable for each image, resulting again in lower resolution.

SUMMARY OF THE INVENTION

The present invention provides an apparatus and method for viewingcomputer generated images with a variety of display characteristicseasily modifiable and with a high resolution bicolor lcd available, andfor inexpensively tracking the positions of the user's head and hand.

The tracking invention in one alternative includes a frame element forthe head tracking of a user whose bodily movement is constrained to asmall area. In a particular embodiment the tracking frame is mountableon a chair, in which the user would sit. Short range and inexpensivetracking elements are deployed for tracking the position of the user'shead; these tracking elements are deployed partly on the user's head andpartly on the tracking frame. The electronics for tracking and userinput are enclosed in a mobile pack, placed near the user or affixed tothe chair. In another particular embodiment, some of the hand trackingelements are located near the head, and hand tracking is referenced fromthe head. This limits the range of hand tracking to an arm's lengthradius, which further simplifies the electronics and processinginvolved. In yet another alternative of the tracking invention sensorsare employed which use natural forces such as gravity, the Earth'smagnetic field, and inertia as their reference, so additional referencesare unnecessary. In a particular embodiment of the invention directed tothe display, the head mounted display allows for interchangeable opticalelements so that the display characteristics may be tailored to suit theneeds of a particular user or application. One optical element disclosedis a bicolor polarizer which allows an lcd to inexpensively provide abicolor display without loss of resolution.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a particular embodiment of a virtualreality system.

FIG. 2 is a side perspective view of a particular embodiment of atracking hood according to the present invention.

FIGS. 3a, 3b and 3c illustrate a particular embodiment of a collapsibletracking hood according to the present invention.

FIG. 4 illustrates a particular embodiment of the Head Mounted Displaywith bar coding for optical tracking of the head's yaw and pitch.

FIG. 5 is a spring loaded frame with interchangeable optical elementsfor use in an HMD.

FIG. 6 illustrates the effect of a bicolor polarizer on light.

FIGS. 7a and 7b are particular embodiments of the tracking frame.

FIG. 8 is an alternative embodiment of the tracking frame.

DETAILED DESCRIPTION OF THE SPECIFIC EMBODIMENTS

FIG. 1 is a block diagram of a virtual reality system, and FIGS. 2through 5 of the drawings depict various particular embodiments of thepresent invention for purposes of illustration only. One skilled in theart will recognize from the following discussion that alternativeembodiments of the structures and methods illustrated herein may beemployed without departing from the invention.

Reference to FIG. 1 is helpful for an understanding of the presentinvention. World Model 10, information which is stored in a storagedevice such as magnetic disk or an interchangeable ROM cartridge, islinked to the Interaction Decision and Control Module (IDCM) 20, whichincludes a host computer and appropriate software. IDCM 20 in turn islinked to the Video Rendering Subsystem 30 and Audio Rendering Subsystem40, which typically comprise special coprocessors. These two renderingsubsystems 30 and 40 are also linked to the Video and Audio DisplaySubsystem (VADS) 100, which generally includes a Head Mounted Display(HMD) and appropriate drivers. The visual display portion of the HMD isusually an lcd; but in some particular embodiments is a liquid crystalshuttered (LCS) crt (LCSs are available from Tektronix, Inc. ofBeaverton, Oregon), and in alternative particular embodiments is aPrivate Eye (available from Reflection Technology, Waltham Mass.).Tracking Subsystem (TS) 200 and User Input Subsystem (UIS) 300 areclosely related and both provide information to IDCM 20: TS 200 isresponsible for tracking the position and/or orientation of the user'shead and other body parts, whereas UIS 300 is responsible for moreconscious forms of input from the user, such as through DataGloves,DataVests, DataSuits, or a variety of other devices including eyetracking devices, voice recognition devices, video tracking devices,keyboards and other conventional data entry devices, pneumatic devices(oral sip and puff), facial expression sensors (optical, fiberoptic,electromyometric), sensors for biological data such as temperature,heart rate or blood pressure, joysticks, pressure sensitive floormats,etc. One example of a virtual reality system can be found in U.S. patentapplication Ser. No. 535,253 filed Jun. 7, 1990 entitled Virtual RealityNetwork incorporated herein by reference.

In a particular embodiment of the present invention as directed totracking, VADS 100, TS 200 and UIS 300 are closely linked physically, soa dotted line has been drawn around them in FIG. 1. FIG. 2 illustrates akey feature of TS 200 in this embodiment, which is a tracking frameformed as hood 210. Tracking hood 210 is shaped to partially surroundthe user's head, and it may be used to limit the freedom of movement ofthe user's head so that shorter range tracking sensors may be used.Position tracking elements are disposed on the hood and on the user'shead. The particular embodiment shown in FIG. 2 employs transmitter 220and receivers 230 and tracking is performed as described in U.S. patentapplication Ser. No. 317,107, entitled computer Data Entry andManipulation Apparatus, incorporated herein by reference and commonlyowned. The close proximity of the position tracking elements on theframe to the position tracking elements on the head allow the use of anyvariety of optical, infrared, or ultrasonic short range inexpensivesensors known to those skilled in the art. In embodiments where HMD 110is strapped to the user's head, the tracking elements disposed on thehead are preferably incorporated into the HMD. In an alternativeembodiment the head tracking is done through spring loaded strings onpulleys disposed on the frame and attachable to a mounting on the user'shead. Potentiometers or shaft encoders within the pulleys thenaccurately and inexpensively track the head's movements. In a particularembodiment of the present invention directed to the hand trackingsystem, such is achieved through similar spring loaded string pulleysincorporated into the head tracking frame, which further simplifies thetracking and input process.

FIG. 4 illustrates another embodiment of the head tracking system, wherea counterbalanced HMD 110 includes bar coded strips 225 and 226 whichare read by optical sensors on the tracking hood for measuring thehead's pitch (rotation about the left-right horizontal axis) and yaw(rotation about a vertical axis). Limiting tracking to the head's pitchand yaw allows the use of very inexpensive sensors and greatlysimplified software. In an embodiment with even cheaper graphics theuser's virtual viewpoint is kept eye-level with the horizon and objectsare arranged to straddle the horizon. Only the head's yaw is tracked, sorelatively few views of the object may be perceived. Only image scalingand block image transferring (blitting) are necessary, resulting ingraphics that can be handled by an inexpensive processor.

Further alternative embodiments are shown in FIGS. 7a, 7b and 8. FIG. 7ashows frame 240 with support members 216, sensors 230, backing 212, andclamps 216. FIG. 7b shows frame 250, similar in design but with stand217 for resting on a desk or similar structure. FIG. 8 shows portableframe 260, which dismantles into hollow rods 263, connectors 261, 262,and elastic retaining cords 264. Sensors 230 respond to head trackingtransmitter 265 and hand tracking transmitter 266.

Other alternative embodiments of the head tracking system do not requirea tracking frame, but instead use natural forces present in the world asreferences. The sensors for these embodiments are disposed on theperson's head. One such alternative embodiment employs tilt sensors(available from Technical Designs, Inc. of Seattle, Wash.), which usegravity as a reference and provides the head's yaw and pitch. Anotheralternative embodiment employs electronic compasses and provides thehead's yaw. Yet another alternative embodiment employs accelerometersand with appropriate software provides the head's x, y and z coordinatesrelative to the starting position, as well as yaw, pitch and roll. Aparticular embodiment of the invention directed to yaw. Only tracking(for blit graphics), as mentioned above, employs an electronic compassfor head yaw tracking. Another particular embodiment of the presentinvention as directed to hand tracking systems employs accelerometers ona glove for hand tracking.

FIGS. 3a, 3b and 3c illustrate a particular embodiment of the headtracking system: collapsible tracking hood 210, with clasps 211 suitablefor mounting onto a chair, and support frame 212. Arcuit members 213 arecovered by sheath 214 and pivot at a common point so they may collapsetogether. Sheath 214 is opaque to reduce ambient light which mightinterfere with optical head tracking systems. For different mountingpurposes, different clasps can be used instead of those shown.

An embodiment of the invention directed to the display involves the HMDand is illustrated as display element 119 in FIG. 5. FIG. 5 shows frame120, which is part of the HMD and is positioned between the lcd and theuser's line of sight. Expandable frame 120 holds various opticalelements which may be interchanged; it includes front retaining bezel121 towards the user's eyes and rear retaining bezel 122 towards the lcdelements, connected by spring loaded connectors 123 so that it mayexpand to accommodate the selected optic elements. Element 130 replacesthe analyzer of the lcd and is an interchangeable polarizer; it may be anormal monochrome analyzer, a color masked analyzer, or a bicoloranalyzer as described below, whichever better suits the user or virtualenvironment. Interchangeable filter 140 may be a diffusion screen orother optical element desired by the user. Interchangeable lens 150allows modification from application to application of whether both eyeshave separate images or share the same one. The selection of lens 150also determines the angle which the image subtends on the user's eye,allowing adjustment of the angular resolution versus the angular fieldof view. In a particular embodiment of this invention theinterchangeable optical elements are coded so that IDCM 20 and VADS 100may automatically account for the selected display characteristics.

In a particular embodiment of the present invention directed to amulticolored display, an lcd is used wherein the second polarizer is abicolor polarizer. Alternatively, the first polarizer may be a bicolorpolarizer and the second polarizer a normal polarizer. A bicolorpolarizer is made of two colored polarizing swatches, each of whichtransmits all wavelengths in one polarization angle but only onewavelength, or a limited range of wavelengths, perpendicular to that(such polarizers are available in a variety of colors from SanritsuElectric Co., Habashi-Ku, Tokyo, Japan). These two swatches are placedwith their selective transmission axes perpendicular to each other, sothat at one polarization angle light of one frequency is transmitted andat a second polarization angle perpendicular to the first, light of asecond frequency is transmitted. FIG. 6 illustrates this operation:incoming white light has components in the α direction (angle), and inthe β direction (angle). Colored polarizer 101 passes all light in the adirection, but blocks everything but green light in the β direction.This light continues to colored polarizer 102 which passes everything inthe β direction and blocks everything but red in the α direction. Theresulting light has only red light in the α direction (angle), and onlygreen light in the β direction (angle). Used as one of the polarizers ofan lcd, this results in a red against green display.

In an embodiment of the present invention directed to tracking, theclose interaction between the VADS 100, TS 200 and UIS 300 is aided byplacing all electronics for these subsystems in a mobile unit which maybe placed near the tracking hood and connected to it by cable. Thisclose placement increases speed of operation and reduces noise. Unitizedenclosure allows cost reduction through shared electronics. In aparticular embodiment this mobile unit is housed within a backpack uponwhich the tracking hood is mountable.

The foregoing is the description of particular embodiments of theinvention. It should be understood that specific details, such ascomponent types, have been provided to explain the construction of theinvention. The scope of the invention may be determined from theappended claims.

What is claimed is:
 1. A virtual reality system usable for presenting avirtual scene to a person, comprising:a head-mounted display usable fordisplaying said virtual scene; a hood-shaped frame disposed about theperson's head; a plurality of receiver elements included in thehood-shaped frame; a transmitter included in the head-mounted display;wherein the transmitter and the plurality of receiver elements areusable to determine a position of the person's head relative to thehood-shaped frame; wherein the transmitter and the plurality of receiverelements are usable to determine at least one component of anorientation of the person's head relative to the hood-shaped frame. 2.The virtual reality system of claim 1, wherein the plurality of receiverelements are bar-coded strips.
 3. The virtual reality system of claim 1,wherein the transmitter is an optical transmitter.
 4. The virtualreality system of claim 1, wherein the transmitter is an ultrasonictransmitter.
 5. A frame for use in a system to determine a position of aperson, comprising:a plurality of tracking elements; and a hood-shapedsupport system for supporting the plurality of tracking elements,wherein the hood-shaped support system at least partially surrounds theperson's head; wherein the plurality of tracking elements are usable totrack a position and at least one component of an orientation of theperson's head relative to the hood-shaped support system.
 6. A frameaccording to claim 5, wherein the frame includes a plurality ofadjustable arms.
 7. A frame according to claim 5, further comprising astand for holding the hood shaped support system.
 8. A frame accordingto claim 7, wherein the stand includes three legs.
 9. A frame accordingto claim 7, wherein the stand is for resting on a table.
 10. A sameaccording to claim 5, further comprising a clamping system, connected tothe hood shaped support system, for clamping the hood shaped supportsystem to a chair.
 11. A frame according to claim 10, wherein theclamping system includestwo clamps for clamping to the chair.
 12. Aframe according to claim 5, further comprising means for determining aposition of the person using the plurality of tracking elements.
 13. Aframe according to claim 5, wherein the tracking elements are sensorsand a transmitter is mounted to the person's head.
 14. A virtual realitysystem usable for presenting a virtual scene to a person, comprising:adisplay usable for displaying said virtual scene; a hood-shaped framedisposed about the person's head; a plurality of tracking elements;wherein the plurality of tracking elements are usable to determine aposition of the person's head relative to the hood-shaped frame; andwherein the plurality of tracking elements are usable to determine atleast one component of an orientation of the person's head relative tothe hood-shaped frame.
 15. The virtual reality system of claim 14,wherein the plurality tracking elements comprises a plurality oftransmitter elements and a plurality of receiver elements.
 16. Thevirtual reality system of claim 15, wherein the plurality of receiverelements includes bar-coded strips.
 17. The virtual reality system ofclaim 15, wherein the plurality of transmitter elements includes opticalsensors.
 18. The virtual reality system of claim 15, wherein theplurality of transmitter elements includes ultrasonic transmitters. 19.The virtual reality system of claim 14, wherein the plurality oftracking elements is mounted to the hood-shaped frame.
 20. The virtualreality system of claim 14, wherein the plurality of tracking elementsis mounted to the display.